U.S. patent number 4,547,415 [Application Number 06/510,876] was granted by the patent office on 1985-10-15 for binderless ceramic or ceramic oxide hollow body and method for its manufacture.
This patent grant is currently assigned to Langlet, Weber KG, Vereinigte Aluminium-Werke Aktiengesellschaft. Invention is credited to Werner Schultze, Knut Weber, Jr..
United States Patent |
4,547,415 |
Schultze , et al. |
October 15, 1985 |
Binderless ceramic or ceramic oxide hollow body and method for its
manufacture
Abstract
This invention relates to a ceramic or ceramic oxide hollow body
and a method for its manufacture. The ceramic or ceramic oxide
hollow body of the present invention does not require the use of a
binder or adhering substrate or any type of internal embedded
supports. The hollow body is capable of being manufactured for any
desired diameter and length and is especially suited for thick
walled pipes. The ceramic hollow body is homogeneous, free of
internal cracks, and highly heat stable and shock insensitive. It
is produced in a continuous quasi-isothermal thermal spray process
in which hot atomized ceramic or ceramic oxide particles are
sprayed as a plasma onto a non-adhering highly thermally conductive
internally cooled mold core. The mold core is mounted on a rotating
lathe which in turn is mounted on a longitudinally movable carriage
to accomplish the uniform layer thickness of the hollow body. The
mold core is removable from the hollow body and the hollow body
thus removed is capable of being directly used without
sintering.
Inventors: |
Schultze; Werner (Bonn,
DE), Weber, Jr.; Knut (Wiehl, DE) |
Assignee: |
Vereinigte Aluminium-Werke
Aktiengesellschaft (both of, DE)
Langlet, Weber KG (both of, DE)
|
Family
ID: |
6092163 |
Appl.
No.: |
06/510,876 |
Filed: |
September 27, 1983 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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225191 |
Jan 15, 1981 |
4460529 |
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Foreign Application Priority Data
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Jan 16, 1980 [DE] |
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3001371 |
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Current U.S.
Class: |
428/34.4;
428/697; 428/698; 428/702 |
Current CPC
Class: |
B28B
1/32 (20130101); B28B 21/44 (20130101); Y10T
428/131 (20150115) |
Current International
Class: |
B28B
1/30 (20060101); B28B 1/32 (20060101); B28B
21/00 (20060101); B28B 21/44 (20060101); B07D
007/22 (); B07D 001/36 (); B05D 003/02 () |
Field of
Search: |
;428/36,690,697,698,702 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kittle; John E.
Attorney, Agent or Firm: Darby & Darby
Parent Case Text
This is a division of application Ser. No. 225,191, filed Jan. 15,
1981, now U.S. Pat. No. 4,460,529.
Claims
What is claimed is:
1. A hollow tubular body comprising layers of fused particles, said
particles being selected from the group consisting of ceramic and
ceramic oxide particles, said particles being free of any binding
agent, said body being porous, free of internal adhering supports,
and said body having been produced under temperature conditions
such that the temperature gradient to which said layers are
subjected does not exceed 2.degree. C./mm of layer thickness.
2. A hollow body according to claim 1 wherein said body has an
exterior wall thickness greater than about 5 mm.
3. A hollow body as defined in claim 2, said body being
impermeable, highly heat stable, shock resistant and free of
internal cracks.
4. The hollow tubular body according to claim 1, wherein said
particles are made of a ceramic material selected from the group
consisting of the carbides, borides and nitrides of aluminum and
titanium, and mixtures thereof, said ceramic material being at
least 99 weight percent pure.
5. The hollow tubular body according to claim 1, wherein said
particles are made of a ceramic oxide selected from the group
consisting of aluminum oxide, magnesium oxide, titanium oxide and
mixtures thereof, said ceramic oxide being at least 99.5 weight
percent pure.
Description
BACKGROUND OF THE INVENTION
This invention relates to a binderless ceramic or ceramic oxide
hollow body and a method for its manufacture.
Ceramic or ceramic oxide hollow bodies are used for calcining
pipes, as containers for highly toxic and radioactive materials and
wastes and as fire resistant linings, pipe insulation and high
temperature process pipes in many industries. The microporous
structure of the ceramic hollow body provides high temperature
stability.
Ceramic materials may be formed into hollow bodies by a variety of
conventional processes such as dry pressing, wet extrusion, slip
molding, isostatic pressing, hot pressing, and injection pressing.
In the dry pressing processes a ground ceramic powder is dry-mixed
with an organic binder, such as dextrin, and subjected to high
pressures on the order of 1000 atmospheres inside steel molds. In
wet extrusion processes the ceramic powder and binder are
slurry-mixed and extruded through nozzles in a plastic
consistency.
Conventional processes require the hollow body to undergo high
temperature sintering to achieve mechanically strong products. The
sintering step is generally conducted in gas-fired tunnel furnaces
or kilns at temperatures on the order of 1650.degree. C. to
1850.degree. C. This sintering process prevents cost effective
manufacture of large diameter and/or long hollow bodies due to the
prohibitive cost of the associated furnaces or kilns.
Another process for producing ceramic oxide hollow bodies is known
as flame spraying as described in W. German Pat. No. 1,646,667. The
ceramic oxide powder is atomized at high temperature resulting in a
partial or complete change in its state of aggregation. The
atomized particles are sprayed onto a rough surface of a solid
substrate. This substrate acts as a binder. The particles bind to
each other and with the substrate. This process presents
disadvantages when thick-walled hollow bodies are required,
because, as the ceramic oxide layers build up there is no longer
any available surface area on the substrate to aid in bonding. As a
result the outer layers tend to detach from the inner bound layers.
In addition, due to the non-uniform temperature gradient between
the substrate-ceramic layer and the purely ceramic layers internal
cracks develop in the body. This leads to lower mechanical strength
for the hollow body and increased permeability. The increase in
permeability may result in leakage due to diffusion of gases or
liquids from the interior through the hollow body. This process has
not, therefore, been found to be effective when thick walled
impermeable ceramic or ceramic oxide hollow bodies such as thick
walled pipes are required.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to produce a
purely ceramic or ceramic oxide hollow body which does not have any
of the physical disadvantages of the prior art. The ceramic hollow
body of the present invention does not require the use of any
binder or binding substrate. The hollow body is homogeneous,
microporous, highly heat stable and shock insensitive.
A second object of the invention is to produce a mechanically
strong hollow body without the need for preformed or
post-production sintering.
Another object of the invention is to produce a thick walled
ceramic or ceramic oxide hollow body pipe having a wall thickness
greater than 5 millimeters which presents no outer layer detachment
and free of internal cracks.
A further object of the invention is a quasi-isothermal thermal
spray process for ceramic or ceramic hollow bodies utilizing an
internally cooled non-binding removable mold core selected for its
high thermal conductivity in relation to the ceramic or ceramic
oxide material to be used.
The term quasi-isothermal as used herein refers to a process in
which the temperature gradient from the flame spraying zone to the
cooling zone of the mold core does not exceed 2.degree. C. per
millimeter of the ceramic or ceramic oxide layer. The
quasi-isothermal process results in uniform purely ceramic or
ceramic oxide hollow bodies of high mechanical strength without
internal cracks.
DESCRIPTION OF THE DRAWINGS
The objects of the process for manufacturing binderless ceramic or
ceramic oxide hollow bodies of any desired dimension will become
more apparent in reference to the accompanying FIGS. 1 and 2.
FIG. 1 is a perspective view, reduced in size, of a pipe of ceramic
or ceramic oxide produced by the present invention.
FIG. 2 is a top view of the equipment used to manufacture the pipe
shown in FIG. 1.
The pipe 1, shown in FIG. 1, consists only of ceramic or ceramic
oxide material. In particular, it contains no binders or mechanical
supports in the form of internal or embedded pipes or cross
connections nor does it require any binding substrate. Any ceramic
or ceramic oxide material which can be applied by thermal spraying
may be chosen. The chemical composition of a typical ceramic body
composition preferred for use in the present invention comprises
aluminum and titanium carbides, borides and nitrides and mixtures
thereof having a purity of at least 99%. The ceramic oxides which
may be employed are e.g. magnesium, aluminum and titanium oxides
and mixtures thereof having purities in the range of at least
99.5%. The choice depends on the intended purpose of the hollow
body. The pipe is porous and its length, diameter and wall
thickness can be freely selected.
The pipe 1 is made by a thermal spraying process on the equipment
shown in FIG. 2. The equipment is constructed in the nature of a
lathe. A carriage 3 is slidably movable along the bed 2 of the
lathe in the longitudinal direction. At the front wall 10, the
carriage 3 carries a rotatable chuck 4, which holds a hollow mold
core 5. The hollow mold core 5 is selected so that its length is
greater than or equal to the length of the desired hollow body and
its outer diameter is the same as the desired inner diameter of the
resulting hollow body. The mold core 5 is cooled internally by a
flowing fluid (e.g. water) flowing through duct 12. The core
material is selected so that its thermal conductivity is such that
in relation to the ceramic or ceramic oxide material of the hollow
body rapid uniform heat transfer is accomplished to maintain the
quasi-isothermal nature of the process. The thermal spraying
equipment 6 is positioned in close proximity to the mold core 5 at
a selected distance to enable its spray nozzle 8 to distribute an
even layer of ceramic or ceramic oxide through the plasma jet onto
the exterior mold core surface. The spraying equipment 6 is also
positioned to enable it to be moved in the radial 15 and axial 15
direction relative to the mold core. This construction allows the
spraying operation to proceed by rotation of the mold core alone,
and axial movement of the thermal spraying equipment. Alternatively
the mold core may be rotated and move axially 13 by the carriage 3
while maintaining the thermal spraying equipment stationery.
The ceramic or ceramic oxide powder is fed into the thermal
spraying equipment and heated such that atomized non-aggregated
ceramic or ceramic oxide particles in the form of a plasma are
sprayed onto the mold core. The particles are uniformly and
continuously sprayed onto the mold core to form a layer of constant
thickness, selected to be between 0.05 to 0.15 mm, on the mold core
while maintaining a quasi-isothermal temperature gradient. Upon
being subjected to the much colder surface of the mold core, the
plasma particles become fused together, but do not fuse to the mold
core. The heat of the particles is rapidly conducted away from the
ceramic or ceramic oxide layer through the mold core and carried
away by the flowing cooling fluid.
An exterior cooling device 7 is located parallel to the axis 12 of
the mold core and ceramic or ceramic oxide hollow body. This device
contains a series of axially extending nozzles 9 for application of
a stream of compressed gas onto the exterior of the ceramic or
ceramic oxide layer. The exterior cooling device 7 serves two
important functions. It is used after the ceramic layer has fused
to remove loose nonbound ceramic or ceramic oxide dust particles
which have reflected off of the surface of the mold core, and have
cooled by the ambient air and redeposited as a non-adhering layer
on the ceramic fused layer. The ceramic dust particles must be
removed prior to depositing each additional layer of ceramic or
ceramic oxide when a thicker wall body is required. If the dust is
not removed prior to the addition of the next layer the
homogeneity, microporous structure and mechanical and thermal
stability of the hollow body would be reduced. This exterior
cleaning of repeated after each successive layer of ceramic is laid
down. As the thickness of the ceramic layers builds up, in order to
maintain the quasi-isothermal temperature gradient the temperature
of the internal cooling fluid is accordingly lowered taking into
account the reduced thermal conductivity of the ceramic layered
core. In addition to reducing the internal cooling fluid
temperature, the exterior cooling device may be used to circulate
cool compressed gas onto the outer surface of the successive layer
of hollow body. As a result of the combined action of the internal
cooling fluid and the exterior compressed gas, quasi-isothermal
operation can be maintained when wall thicknesses greater than 5 mm
are desired.
The internal cooling fluid may be a liquid compatible with the mold
core material and having a suitable temperature differential
between its operating temperature and its bubble point or critical
temperature such that its temperature can be raised when subjected
to the heat transferred from the mold core without expanding
rapidly and distorting the shape of the mold core. The internal
cooling fluid is preferably water. The direction of the cooling
fluid is preferably countercurrent with the axial direction of the
thermal spraying. Other coolants such as low melting salt mixtures,
and thermo oils such as Therminol.sub.R type 60 having a range of
use from -60 to +600 degrees F. or Therminol.sub.R type 80 having a
range of use from 300 to 750 degrees. These therminol oils are sold
under the above trademarks registered to the Monsanto
Corporation.
The external compressed gas must be directed with a velocity
sufficient for cleaning and cooling. It must be directed arcuately
to the surface of the hollow body in such a way as to be
distributed uniformly over the entire exterior surface. It is
preferred that the compressed gas be at a pressure in excess of 1
atmosphere. Air nitrogen and carbon dioxide are examples of three
preferred gasses for use in the invention.
The mold core may be constructed of metallic or non-metallic
materials having good thermal conductivity and which are
non-adhering to ceramic or ceramic oxides. Metallic mold core
materials found suitable for this process include all pure metals
and alloys with a high coefficient of expansion, such as copper,
aluminum, alloys of aluminum and beryllium (Al 95.8%, Be 4.2%),
aluminum and magnesium (Al 85.9%, Mg 12.7% remainder Si, Fe and Co)
or magnesium and aluminum (Mg 90-96%, Al 10-14%). The preferred
metallic mold core material is aluminum. Non-metallic mold cores
found to be satisfactory are cardboard, wood or plastic having a
non-adhering heat resistant layer of glass fiber-coated
polytetra-fluoroethylene (Teflon) or heat resistant textiles in the
form of tapes or sheets, and contact with the ceramic. In such
cases the cardboard must be protected from the high temperatures by
very strong internal cooling. These mold cores can be separated
from the hollow body by shrinkage or by destruction such as, for
example, by combustion of the cardboard. Whatever mold core
material is selected it must not bind with or cling to the ceramic
material.
The detachability of the mold core from the hollow body can be
assured by the choice of a core with a higher coefficient of
expansion relative to that of the ceramic or ceramic oxide layer or
by the construction of the core as an expanding mandrel. It is
preferred to select a mold core which can be re-used to manufacture
additional pipes.
After the desired wall thickness of the ceramic or ceramic oxide
hollow body is achieved it is removed from the core. This can be
accomplished for example by shrinking the core or constructing the
core as an expanding mandrel. The next ceramic pipe body can then
be sprayed on the mold core. Upon removal the hollow body can be
immediately transported and used without a final sintering
operation. Sintering may become desirable when hollow bodies with
wall thickness in excess of 20 mm are required.
* * * * *